Paper coater blowoff apparatus

ABSTRACT

A paper coater for providing a uniform coating on the surface of a traveling web using an air knife to control the coating thickness and finish, having a blowoff box and related separator and suction mechanisms arranged to completely trap, collect and separate the mist and its components resulting from air knife operation. The blowoff box has a number of vortex suppressor means and spoilers cooperatively related to deliver coating material for return to the coating material supply tank and to collect mist and separate its waste components and air for discharge respectively, to sewer and atmosphere, eliminating mist discharge into the environs of the paper-making machinery of which the coater forms a part.

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per-making machinery of which the 2,279,553 4/1942 118/63 X coater forms a part.

PATENTED um 1 2197i SHEU 2 UF 2 Smm mfr. WM @W J V PAPER COATER BLOWOFF APPARATUS BACKGROUND OF THE INVENTION l. Field ofthe Invention The invention relates to paper-coating equipment and more particularly to blowoff apparatus for a paper coater which eliminates the` discharge into the atmosphere and around papermaking equipment of mist originating from operation of an air knife to control the coating applied to a surface of a traveling web.

2. Description of the Prior Art Paper coaters using air knives to smooth the coating layer applied to a traveling web have been equipped with blowoff devices intended to collect mist resulting from air knife operation. However, all known prior devices are inefficient and do not prevent the escape of mist from and around the coater. Also the prior devices are inefficient in salvaging coating material blown by the air knife from the traveling web, and do not provide for separation of mist from its air and for discharge of waste mist components to sewer.

SUMMARY OF THE INVENTION Objectives of the invention are to provide a paper coater blowoff system which reduces foaming and eliminates misting or the escape of mist from the blowoff box; which contains all airflow coming from the air knife and salvages as much coating material as possible and returns it to the circulating tank which serves as the coating material supply for the coater; which reduced buildup of dry coating material or color in the system thereby reducing washup frequency; which eliminates the discharge of fumes from the coater and blowoff box; which contains all mist including finely divided dry particle components of the mist within the system, separates the same from the air passing through the system for runoff to sewer; which includes a blowoff box that may be opened readily for inspection and cleaning, and which blowoff box or a part thereof may be moved away from the backing roll and traveling web for ready access to the blowoff box; and which obtains the stated objectives simply, and solves problems and satisfies needs existing in the art.

These objectives may `be obtained by the blowoff system which may be stated in general terms as including blowoff box means for a paper coater, comprising walls forming a suction chamber and walls forming a smaller coating material collector chamber within the suction chamber; said collector chamber walls forming a top opening located below and communicating with a top opening formed by the suction chamber walls; said blowoff box preferably being formed of separable sections exposing at lest the interior of the suction chamber when separated; backup roll means including a roll axis around which a traveling paper web moves; means for applying coating to the surface of the web; air knife means adjustably mounted adjacent the backup roll means for controlling and finishing a coating layer previously applied to the traveling web; the blowoff box means being located in normal operating position with its suction chamber top opening matching the contour in cross section of the backup roll; spoiler blade means mounted within the blowoff box means extending parallel with the axis of the backup roll means and spaced a fixed distance away from the backup roll means and extending transverse of the suction and collector chamber openings and into said suction and collector chambers; vortex suppressor baffle means extending parallel with the axis of the backup roll means within the collector chamber; a coating material return conduit connected with the collector chamber and communicating with coating material circulating tank means; exhaust fan means; mist separator means; a suction conduit communicating with the suction chamber and the mist separator means; the exhaust fan means communicating with the mist separator means to draw air drawn into the suction chamber and air discharged by the air knife and mist formed thereby from the suction chamber through the separator means; the separable blowoff box sections including an upper section containing the collector and suction chamber opening forming walls; means mounting said upper box section for movement toward and away from the backup roll means, whereby said upper section may be moved out of normal operating position to expose to access the suction and collector chambers, the spoiler blade means and the vortex suppressor baffles; and means for moving at least the upper box section toward and away from the backup roll means.

BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention-illustrative of the best mode in which applicants have contemplated applying the principles-is set forth in the following description and shown in the drawings and is particularly and distinctly pointed out and set forth in the appended claims.

FIG. l is a fragmentary diagrammatic view of the improved blowoff apparatus in normal or operating position;

FIG. 2 is a view similar to FIG, l but showing the blowoff box in retracted position;

FIG. 3 is an enlarged diagrammatic sectional view of the blowoff box illustrating the manner in which air currents therein are controlled and directed;

FIG. 4 is a fragmentary view similar to a portion of FIG. 3, showing the air knife adjusted to a different angle of inclination and a modified arrangement of the suction chamber opening defining walls;

FIG. S is a section looking in the direction of the arrows 5- S, FIG. 3;

FIG. 6 is a section taken on the line 6-6, FIG. 5; and

FIG. 7 is a fragmentary view looking in the direction of the arrows 7-7, FIG. 3.

Similar numerals refer to similar parts throughout the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The web, indicated generally at l traveling in the direction of the arrows 2 through a paper coater generally indicated at 3 in a papermaking machinery line, has a coating 4 applied to a surface thereof by a typical coating roll 5 receiving coating material 6 contained in a pan 7 in a usual manner.

The traveling web l in its course of movement with coating material 4 on its surface, passes around a backup roll 8 where an air knife generally indicated at 9 is used to control the thickness, finish, uniformity, smoothness, etc. of the previously applied coating 4.

Air knife 9 may be constructed, arranged, and mounted for various controls and movements as set forth in the J. B. Kohler U.S. Pat. No. 3,314,163 so that its angle of impingement I0, its lip-to-roll distance, its nozzle opening, etc., may be varied. Also air knife 9 is adapted for movement toward and away from backup roll 8 as indicated by double-headed arrow II, so that in retracted position illustrated in FIG. 2, the nozzle lips may be opened for cleaning as indicated by dot-dash lines 12. The various mountings, adjustments, and controls for the air knife 9 may include a linkage system (not shown) such as disclosed in U.S. Pat. No. 3,314,163.

The angle of impingement l0 of the air jet discharged by the nozzle of air knife 9 is illustrated in FIGS. l and 3 as being 50. This angle is the angle between the centerline of the jet passing through the point of impingement 13, and a radial line 14 passing through the axis 8a of backup roll 8 and the point of impingement 13. Normally, the range of adjustment of the angle of impingement may be from 30 to 60.

The operation of an air knife 9 in controlling the coating thickness and finish in a paper coater 3 normally produces a mist. Paper coaters usually are provided with a blowoff box for collecting and disposing of the mist as well as the excess coating material removed from the web by air knife operation. Heretofore, numerous blowoff box arrangements have been used to collect and dispose of the mist and removed coating material but these prior devices have been very inefficient.

parting relative movement to the suction chamber sections I9 lo and 20.

The suction box I5 may be supported and moved by any desired lifting or supporting or conveying equipment, as by mounting the same on a cylinder a connected with the lever and linkage system which supports and mounts the air knife. Vertical movement of suction box l5 in either direction is indicated by the double-headed arrow 23 in FIGS. l and 2 and horizontal movement thereof is indicated by the doubleheaded arrow 24 in FIG. 2. Blowoff box 15 when in raised or operating position is located at the proper position with respect to backup roll 8 by locator means 25 which engage stops 26 carried by blowoff box l5 preferably at either end thereof.

The separable suction chamber sections 19 and 20 are properly located with respect to each other when connected and sealed as in FIGS. l and 3 by locator means 27 carried by lower suction chamber section and pins 28 carried by upper suction chamber section 19 preferably at either end thereof. When the blowoff box l5 is in retracted position of FIG. 2, upper section I9 may be raised slightly from lower section 20 to separate the sealed joint 22. When the sections 19 and 20 are separated in retracted position (FIG. 2), upper section I9 may be moved in any suitable manner such as along a track 29 to the dot-dash position indicated at 30 when both ends of the upper suction box section 19 and its interior are accessible for cleaning, etc.

Suction conduit 2l preferably has a flexible hose connection 3l with the inlet 32 equipped with a spray line 33 of a separator tank 34 having separator baffles 35 and a removable cover 36. Separator tank 34 has an outlet drain 37 which preferably is equipped with a U-shaped sealing leg 38 connected with a sewer.

A suction pipe 39 connected with the inlet 40 of exhaust fan 4I extends upward within separator tank 34 and exhausts air as indicated by the arrow 42 from the separator 34, which is then discharged from exhaust fan 4l to the atmosphere as indicated by the arrow 43.

Each end wall 18 of blowoff box l5 (FIG. 3) has a curved upper edge 44 (FIG. 3) matching the contour of backup roll 8, as shown. Blowoff box front wall 16 preferably bulges outwardly to the right at 4S below its upper edge 45a, and the convex outward bulge 45 extends generally in a direction opposite to that in which the traveling web is moving.

Blowoff box rear wall 17 extends upward and then is directed laterally upward toward backup roll 8 by a flangelike portion indicated at 46. The flangelike portion 46 along its free edge has an adjustable V-shaped member 47 secured thereto by slot and bolt connections 48. V-shaped member 47 terminates in a reversely turned vortex suppressor baffle 49. Thus, curved edges 44 of the end walls 18, the upper edge 45a of the front wall ll6 and the V-comer of V-shaped member 47 at the upper end of rear wall 17 form a top opening for suction chamber S.

A rear supplementary angular wall 50 is mounted within suction chamber S extending in angular relation to rear wall 17 and a brace or strut wall 51 extends between the walls ll7 and 50 and from end to end between the suction chamber end walls I8. A channellike formed bottom wall 52, having a centrally disposed sump portion 53, is connected with rear angular wall 50. The right-hand uptumed portion of channel bottom wall 52 extends upwardly and flares outwardly at 54 to form an intermediate angular wall spaced from and generally matching the contour of the suction chamber front wall 16 and forming a suction chamber passage between said front and intermediate walls I6 and 54. Wall 54 has a transverse ridge 54a convex toward wall 50 for a purpose to be later described.

A formed channellike member 55 having an upwardly inwardly hooked edge 56 and an upwardly convex lower flange 57 is releasably mounted on wall 54 and forms an upward extension of intermediate wall 54. The releasable mounting is provided by formed plates 58 mounted on the inside surfaces of end walls 18. The ends of channel member 55 rest on the upper edges of plates 58; and the ends of lower flange 57 are notched at 59 (FIGS. 5 and 6) to permit flange S7 to disengage pins 60 projecting inwardly from sidewalls I3 when member 55 is rocked to the left (FIG. 3) along its convex flange 57.

Struts, braces or hand holds 6l spaced at intervals along member 55 extend between the hooked edge 56 and the lower flange 57 to brace these formed portions and impart rigidity to member 55. Hand holds 6l may be grasped and the member 55 moved arcuately counterclockwise to a position where pins 60 may be released through notches 59 so that member 55 may be lifted out of the blowoff box for cleaning the blowoff box structure.

When member 55 is in assembled or working position as shown in FIG. 3, angular rear wall 50, bottom wall 52, flared intermediate wall 54, channel member 55 and its hooked edge 56, and the end walls 18 of blowoff box l5 form a coating material collector chamber C within suction chamber S. Chamber C has a top opening located below and communicating with the top opening of the suction chamber S. The collec tor chamber top opening is defined by the end walls I8, the hooked edge 56, and the V-corner of V-shaped member 47.

The rear and supplemental walls I7 and 50 form rear wall means which acts in common as the rear wall of the collector and suction chambers C and S. The upper edges of the rear wall members l7 and 50 define in common an opening edge for the top collector and suction chamber openings as shown in FIG. 3. The upper top opening edge 56 of the intermediate wall 54-55 is spaced from the front suction chamber wall top opening edge 45a, as shown, to define an opening to the suction chamber passage formed between the front and intermediate walls 16 and 54-55. The exhaust fan 4I, which produces the suction in the suction chamber S, thus has communication with the upper portion of the suction chamber through the suction chamber passage.

Blowoff box I5 in normal operating position (FIG. 3) has the top opening of suction chamber S matching the contour in cross section of backup roll 8 and spaced therefrom generally by the spacing from coated web ll of the top curved edges 44 of end walls I8.

A first, main or primary spoiler blade 62 is mounted within blowoff box l5 extending parallel with the axis 8a of backup roll 8 and has its upper edge comer 63 spaced a fixed distance away from backup roll 8. Spoiler blade 62 extends transversely of the suction and collector chambers S and C and extends into suction chamber S and through the top opening of collector chamber C and into collector chamber C.

A secondary spoiler blade 64 also is mounted within blowoff box l5 extending parallel with the axis 8a of backup roll 8 and has its upper edge 65 spaced a fixed distance away from backup roll 8.

Spoiler blades 62 and 64 preferably are supported at their ends on support plates 66 mounted on the inner faces of end walls 18. One or more brace members 67 may be bolted at flanged edges 68 and 69 of member 67 (FIG. 7) to spoiler blades 62 and 64 to maintain rigidity to and the relatively fixed positions of the spoiler blades 62 and 64. The upper edges of brace members 67 may be formed to have a sharp edge indicated at 70.

Lower flange 57 of member 55 also acts as a vortex suppressor baffle. Baffie members 57 and 49 extend parallel with the axis of the backup roll 8 within collector chamber C.

A coating material return conduit 7l is connected to sump portion 53 of collector chamber C and connects with a suitable pipe, not shown, which extends to a coating material circulating tank of usual construction. Such coating material circulating tank in turn provides the source of supply of coating material 6 for coating pan 7.

An air knife in normal operation removes a portion of the coating 4 previously deposited on the undersurface of web l moving around backup roll 8, to thus form the desired coating thickness, finish, smoothness, etc. Air discharged from the air knife may be at the rate of say 1,200 cubic feet per minute. This air jet in removing coating material, forms a generally liquid stream of removed coating material indicated by the arrow 72. The air jet blowing through the stream of removed coating material separates the stream into stringerlike masses of coating material which fall or are blown generally into collector chamber C and against rear wall 50 in the manner shown by the dotted flow lines 73 in FIG. 3. In general, the plane indicated by arrow 72 defining the general direction in which the coating material is blown from the web by the air jet is at an angle generally the same with respect to radial line 14 as the angle of impingement 10 of the air knife 9. However, the coating material ejected fans out in the zone 73 as diagrammatically illustrated.

Some of the air discharged from air knife 9, when adjusted at the angle 10 as shown in FIG. 3, has a tendency to move clockwise upwardly as shown by the arrows 74 in a somewhat vortexlike fashion. Suppressor baffle 49 suppresses or kills this vortex action so that mist, droplets, etc. contained in the vortex gather or flow at 75 downward in the direction of the arrow toward and along the inside surface of angular wall 50.

Substantially all of the coating material in liquid form removed by the air knife is discharged as shown along area 73 and against wall 50. This liquid coating material flows downwardly along wall 50 as indicated by the arrow 76 to the bottom of collector chamber C and into sump portion 53 where the liquid collects as indicated by the liquid level 77. The liquid coating material collected at 77 in collector chamber C then flows through conduit 71 to a circulating tank as described.

Air knife operation creates a mist of entrained particles or droplets of coating material incident to the removal of liquid coating from the traveling web. Such mist has been the source of most of the difficulties encountered in the past in the operation of air knives and blowoff boxes. The mist deposits and builds up a crust of dry coating material on the surfaces of the equipment. It also permeates the atmosphere surrounding the papermaking equipment in an objectionable manner.

We have discovered that the Coanda Effect of part of the airstream blown from the air knife is at least partially responsible for the escape of mist from prior blowoff boxes, and for the inability to efficiently confine and collect the mist. This C- oanda Effect involves the wall-hugging tendency of a stream of air to hug a surface against which it is directed. Thus, part of the air jet from air knife 9 striking the web undersurface below backup roll 8 tends to hug and flow along the web surface in a direction opposite to that of web movement.

This Coanda Effect is indicated by the arrow 78 in FIG. 3 which represents not only the stream of air hugging the coated surface of the web I but also mist and droplets, etc. of coating material removed from the coating at the line of impingement 13 of the air knife.

In accordance with concepts of the invention, primary spoiler blade 62 has a flat surface 79 located at a slightly acute angle less than perpendicular to tangency with the backup roll in the direction of the oncoming Coanda stream to block passage of the Coanda stream and divert as much as possible of the stream downwardly into the collector chamber C.

The upper edge 63 of primary spoiler blade 62 is located as close as possible to backup roll 8 so as to block most of the air and entrained mist and direct it down into collector chamber C. This spacing normally is not less than about one-eighth inch so that spoiler blade 62 does not interfere with the deposited coating 4 on web l, but the spacing should be as small as possible to maintain maximum constriction of airflow to the C- oanda stream.

Primary spoiler blade 62, because of its spacing away from the traveling web, does permit some air to continue as Coanda" flow past the upper edge 63 of blade 62. This upper blade edge initially has a surface extending from corner 63 parallel to tangency with roll 8. The blade edge then curves rearwardly downwardly as shown at 80. Some of theair and entrained material passing through the space between edge 63 and roll 8 tends by Coanda Effect" to hug curved surface of spoiler blade 62. This directs and discharges the air and entrained coating material and mist downward toward secondary spoiler blade 64 as indicated by the arrow 8l. The material discharged at 8l fans out as indicated at 82 and contains lighter mist and droplets of coating material. These components strike the left-hand face of secondary spoiler blade 64 where liquid coating material collects and runs down into collector chamber C as indicated at 83.

The main stream of coating material diverted by the primary spoiler blade 62 runs down the left-hand face of spoiler blade 62 and into collector chamber C as indicated by the arrow 84.

All of the air and entrained material hugging the roll 8 which passes spoiler blade 62 is not diverted downwardly at 8l, but some continues to hug roll 8. This remaining air again is partially blocked and diverted as indicated by the arrow by the second spoiler blade 64. Spoiler blade 64 has its upper edge 65 spaced from the roll 8 about the same distance as the spacing of primary spoiler blade 62. Secondary spoiler blade 64, however, has a sharp comer as shown, which again diverts most of the remainder of the air and entrained matter passing the upper edge 65 of blade 64, downwardly as indicated by the arrow 86.

The airflow and entrained material indicated at 86 discharges downwardly, as shown by the arrow 87, against and is trapped by channel member 55. Liquid coating material collects at 88 in channel member 5S and flows through openings 89 formed therein (FIG. 5) into the lower portion of collector chamber C, as indicated.

The velocity of any air after passing the upper edge 65 of secondary spoiler blade 64 very low. This condition, and the expansion of the air that has taken place passing through the restricted spaces above each of the spoiler blades 62 and 64, permits the suction from exhaust fan 4l, which subjects the suction chamber S to reduced pressure, to exhaust from the blowoff box the air and entrained mist remaining in the suction chamber S to the right of secondary spoiler blade 64. This air and mist in being exhausted flows through the suction chamber passage between intermediate wall member 55 and the bulged front wall 45 of blowoff box l5 without any escape of air and mist from the blowoff box and particularly without escape of mist between the edge 45a of wall 16 and the moving web.

Meanwhile, air emanating from the air knife, along with coating material either in the form of liquid or mist, deflected by the primary and secondary spoiler blades 62 and 64 into the lower portion of collector chamber C may tend to result in air circulated as a vortex indicated by the arrow 90. However, vortex suppressor baffle 57 truly suppresses or blocks any substantial vortex action. The circular vortex airflow that does take place, as indicated by the arrows 90, tends to throw out particles or droplets of coating material by centrifugal force. This coating material collects in and on the walls of collector chamber C and flows to the bottom thereof. Ridge 54a prevents the vortex 90 from interfering with flow of liquid material through openings 88.

The air itself, and whatever fine mist is entrained thereby, which circulate within collector chamber C flow out of collector chamber C following a path generally as shown by arrows 91. This air and mist then move into suction chamber C and join air and entrained mist previously described as being pulled by suction by exhaust fan 4l from suction chamber S along a path through the suction chamber passage indicated by arrows 92.

The air and mist exhausted from suction chamber S at 92 flows through conduit 21 and hose 31 into separator 34. Usual action takes place in separator 34 wherein mist particles are separated and collect at the bottom of the separator and flow out to sewer, while the separated air is discharged by exhaust fan to atmosphere at 43.

Exhaust fan is operated to pull from 3,600 to 3,700 cubic feet per minute of suction air from the suction chamber S. This is nearly three times the amount of air that is discharged by the air knife into the blowoff box l5. This means that additional air is pulled into the suction chamber around the top opening thereof to collect and retain the mist within the blowoff box wherein the mist components are collected and discharged.

The air knife has been described as being set at an angle of impingement of 50in FIG. 3. When that angle is reduced, to say a 40angle as shown in FIG. 4l, the angle indicated by the line 93 at which coating material is dislodged by the air knife 9 also is reduced. This may eliminate the necessity of using a V- shaped member 47. Member 47 may be replaced by an upper lip plate 94 forming the upper opening of the blowoff box as shown in FIG. 4l.

In other words, the coating material removed as shown in FIG. 4 strikes the collector wall 50 at such an angle that if any vortex is formed by the deflected air, the vortex moves in a counterclockwise direction. In such event, there is no necessity for a vortex suppressor blade, such as the member 49 in FIG. 3 which acts to suppress a clockwise vortex, represented by the arrows 74.

The angle of impingement of air discharged by the air knife 9 may be changed in operation of the equipment for various reasons, since the angle is determined by a number of factors, namely, the viscosity of the coating material, the desired weight of coating to be formed, the speed of the web, and the smoothness to be imparted to the material left on the web. lf the angle, determined by these variables, is such as to produce clockwise rotation of the air within the collector and suction chambers immediately below the air knife, then the vortex suppressor baffle 49 is used. If the angle of impingement of the air knife is such that counterclockwise rotation of the air results as shown in FIG. 4, then lip member 94 will be used.

The basic concept of and the success of the improved blowoff construction in completely eliminating the escape of mist from the blowoff box, resides in the construction, shape, placement and relationship of the spoiler blades 62 and 643 with respect to the other elements. This arrangement successfully blocks and finally turns the Coanda" flow of air along the coated web surface passing around the backup roll, so that substantially all the air and entrained material is turned or redirected into the collector chamber C, and the remaining amount of air emanating from air knife operation, and the fine mist entrained therein, has such reduced velocity and pressure that it is all removed from the suction chamber S by the suction fan 4l.

The blowoff box system and construction involving the concepts of the invention is the first known blowoff box for a paper coater that does not allow the escape of mist, dust, fumes, etc. from the equipment used to carry out an air knife paper coater operation.

The improved construction further is characterized by simplicity in providing the new result; it involves a structure which may be readily removed from operating position, separated into upper and lower sections, and cleaned when necessary with ready accessibility to interior surfaces of the collector and suction chambers, the spoiler blades and vortex Suppressors; and it provides a structure which accomplishes the objectives described, eliminates difficulties encountered with prior devices, and solves existing problems in the art.

In the foregoing description, certain terms have been used for brevity, cleamess and understanding; but no unnecessary limitations are to be implied therefrom beyond the requirements of the prior art, because such terms are used for descriptive purposes and are intended to be broadly construed.

Moreover, the description and illustration of the invention is by way of example, and the scope of the invention is not limited to the exact details, or to the particular structure of some of the elements in the system which have been illustrated diagrammatically` Having now described the features, discoveries and principles of the invention, the manner in which the improved blowoff system is constructed and operated, the characteristics of the new construction, and the advantageous, new and useful results obtained; the new and useful structures, devices, elements, arrangements, parts and combinations, and mechanical equivalents obvious to those skilled in the art are set forth in the appended claims.

We claim:

l. In blowoff box apparatus for a paper coater of a type in which a traveling web having a coating applied to one surface moves around backup roll means having a roll axis, and air knife means positioned adjacent an upwardly moving coated web surface directs in air jet at an angle against the previously coated web surface to control and finish the coating; the combination of blowoff box means including rear wall means, and front and end walls forming a suction chamber; walls including an intermediate wall forming a smaller coating material collector chamber within the suction chamber; the collector chamber walls having portions defining a top opening; the suction chamber front and rear wall means having upper edges, the suction chamber end walls having curved upper edges matching the contour of the backup roll means of a paper coater in normal position of the blowoff box means, and said upper edges defining a suction chamber top opening at a location spaced above the collector chamber top opening and spaced below a coated web traveling around such backup roll means; the suction chamber rear wall means being in common the rear wall means of the collector chamber', the suction chamber opening edge at the top of the rear wall means defin ing in common a portion of the collector chamber opening and being located adjacent and below the paper coater air knife means; the intermediate wall having an upper edge defining another portion of the collector chamber opening, and said upper intermediate wall edge being spaced from and substantially close to the front suction chamber wall upper edge defining an opening to a suction chamber passage formed between said front and intermediate walls; suction means for the blowoff box means communicating with said suction chamber passage; spoiler blade means mounted within the blowoff box means extending parallel with the axis of the backup roll means and spaced a fixed distance away from the backup roll means and extending transversely of the suction and collector chamber openings and into said suction and collector chambers between said intermediate wall and rear wall means; and said spoiler blade means having a flat surface blocking the flow of a substantial portion of air-knifedischarged air which hugs the coated surface of the traveling web passing around said backup roll means and the mist formed by the air-knife-discharged air entrained by said coated-surface-hugging air, and directing said blocked air and entrained mist into said collector chamber.

2. The construction defined in claim I in which vortex suppressor baffle means is mounted within the collector chamber and extends parallel with the axis of the backup roll means.

3. The construction defined in claim ll in which the collector chamber intermediate wall is fiared and the collector chamber rear wall means is angular, and said flared and angular intermediate and rear walls converge to form a connected channel bottom wall forming a sump located within the suction chamber; and in which an upwardly convex curved wall projects from said flared wall into the collector chamber forming a vortex suppressor baffle within the collector chamber.

4. The construction defined in claim l in which an adjustable V-shaped member forms the common opening defining edge of the common suction and collector chamber rear wall means, and in which said V-shaped member has a flange projecting downwardly into the collector chamber forming a vortex suppressor baffle.

5. The construction defined in claim l in which the collector chamber intermediate wall is upwardly flared, in which the rear wall means is angular, in which the rear wall means terminates at the common opening defining edge, and in which the intermediate flared wall terminates in an upwardly inwardly curved opening defining edge.

6. The construction defined in claim l in which the spoiler blade means includes a blade having a top comer and having its flat surface extending at an angle toward the air knife acute with respect to a radial plane passing through the axis of the `backup roll means and through said top corner.

7. The construction defined in claim l in which the spoiler blade means includes a blade having a tip corner, the blade having its flat blocking surface extending from said top corner and facing toward the air knife, and the blade having a curved upper edge extending from said top corner away from the air knife adjacent to but spaced from the traveling web, whereby a portion of the air and mist hugging the web and passing through the space between the spoiler blade and web hugs the curved spoiler blade edge beyond the flat blade surface and is directed into the collector chamber.

8. The construction defined in claim 1 in which the spoiler blade means includes a plurality of spoiler blades each having flat surfaces facing toward the air knife blocking flow of air and entrained mist discharged from the air knife means and hugging the coating surface of the traveling web, in which each spoiler blade has a surface opposite its flat surface, and in which said blades direct air and mist hugging the web into the collector chamber along their flat and opposite surfaces.

9. The construction defined in claim l including a mist separator, means connecting the mist separator with the suction chamber passage, and the suction means being connected with the mist separator to draw air and entrained mist from the blowoff box suction chamber through the suction chamber passage into the mist separator and to discharge air from the mist separator to the atmosphere.

l0. The construction defined in claim l including coating material supply tank means, and conduit means connecting the collector chamber and supply tank means, whereby coating material liquid discharged into and collected inthe collector chamber may be recycled to the supply tank.

ll. The construction defined in claim l in which the suction chamber walls are formed of separable upper and lower sections, in which the upper section contains the rear wall means and the front and intermediate collector and suction chamber walls, and in which mounting means is provided for supporting and moving the upper and lower sections toward and away from the backup roll means, whereby said upper section may be detached from the lower section and moved out of normal operating position for access to the interior of said upper section.

12. The construction defined in claim 1 in which mounting means supports the blowoff box suction and collector chamber walls for movement toward and away from the backup roll means, and in which means is provided for moving said blowoff box walls toward and away from the backup roll means.

13. The construction defined in claim 1 in which vortex suppressor bale means are mounted within the collector chamber extending parallel with the axis of the backup roll means, and in which said vortex suppressor baffle means are removably mounted within said collector chamber.

14. The construction defined in claim 1 in which the air knife means is adjustably mounted to vary its angle of impingement, in which vortex suppressor baffle means extends parallel with the axis of the backup roll means within the collector chamber and below the air knife means, and in which said baffle means is adjustable to coordinate its operation with adjustment of the air knife means,

15. In a coating apparatus blowoff box construction in which a web traveling along backup means and having a coating applied to one surface moves past air knife means directing in air jet at an angle against the coated web surface; the

combination of blowoff box means includinghrear wall means, and front and end walls forming a suction c amber; walls including an intermediate wall forming a smaller coating material collector chamber within the suction chamberjthe collector chamber walls having portions defining a top opening; the suction chamber front and rear wall means having inner edges, the suction chamber end walls having shaped upper edges matching the contour of the backup means, and said upper edges defining a suction chamber top opening at a location spaced above the collector chamber top opening and spaced below a coated web traveling along such backup means; the suction chamber rear wall means being in common the rear wall means of the collector chamber; the suction chamber opening edge at the top of the rear wall means defining in common a portion of the collector chamber opening and being located adjacent and below the air knife means; the intermediate wall having an upper edge defining another portion of the collector chamber opening, and said upper intermediate wall edge being spaced from and substantially close to the front suction chamber wall upper edge defining an opening to a suction chamber passage formed between said front and intermediate walls; suction means for the blowoff box means communicating with said suction chamber passage; spoiler blade means mounted within the blowoff box means extending parallel with the backup means and spaced a fixed distance away from the backup means and extending transversely of the suction and collector chamber openings and into said suction and collector chambers between said intermediate walls and rear wall means; said spoiler blade means having a flat surface blocking the flow of a substantial portion of air-knifedischarged air which hugs the coated surface of the traveling web passing along said backup means and the mist formed by the air-knife-discharged air entrained by said coated-surfacehugging air, and directing said blocked air and entrained mist into said collector chamber; said spoiler blade means including a first blade having front and rear surfaced and a shaped edges between said front and rear surfaces, the front spoiler blade surface being the flat blocking surface and intersecting the shaped edge at a sharp comer, said shaped edge extending from said sharp corner parallel to tangency with the backup means, and said shaped edge then curving rearwardly downwardly to said rear blade surface. 

2. The construction defined in claim 1 in which vortex suppressor baffle means is mounted within the collector chamber and extends parallel with the axis of the backup roll means.
 3. The construction defined in claim 1 in which the collector chamber intermediate wall is flared and the collector chamber rear wall means is angular, and said flared and angular intermediate and rear walls converge to form a connected channel bottom wall forming a sump located within the suction chamber; and in which an upwardly convex curved wall projects from said flared wall into the collector chamber forming a vortex suppressor baffle within the collector chamber.
 4. The construction defined in claim 1 in which an adjustable V-shaped member forms the common opening defining edge of the common suction and collector chamber rear wall means, and in which said V-shaped member has a flange projecting downwardly into the collector chamber forming a vortex suppressor baffle.
 5. The construction defined in claim 1 in which the collector chamber intermediate wall is upwardly flared, in which the rear wall means is angular, in which the rear wall means terminates at the common opening defining edge, and in which the intermediate flared wall terminates in an upwardly inwardly curved opening defining edge.
 6. The construction defined in claim 1 in which the spoiler blade means includes a blade having a top corner and having its flat surface extending at an angle toward the air knife acute with respect to a radial plane passing through the axis of the backup roll means and through said top corner.
 7. The construction defined in claim 1 in which the spoiler blade means includes a blade having a tip corner, the blade having its flat blocking surface extending from said top corner and facing toward the air knife, and the blade having a curved upper edge extending from said top corner away from the air knife adjacent to but spaced from the traveling web, whereby a portion of the air and mist hugging the web and passing through the space between the spoiler blade and web hugs the curved spoiler blade edge beyond the flat blade surface and is directed into the collector chamber.
 8. The construction defined in claim 1 in which the spoiler blade means includes a plurality of spoiler blades each having flat surfaces facing toward the air knife blocking flow of air and entrained mist discharged from the air knife means and hugging the coating surface of the traveling web, in which each spoiler blade has a surface opposite its flat surface, and in which said blades dirEct air and mist hugging the web into the collector chamber along their flat and opposite surfaces.
 9. The construction defined in claim 1 including a mist separator, means connecting the mist separator with the suction chamber passage, and the suction means being connected with the mist separator to draw air and entrained mist from the blowoff box suction chamber through the suction chamber passage into the mist separator and to discharge air from the mist separator to the atmosphere.
 10. The construction defined in claim 1 including coating material supply tank means, and conduit means connecting the collector chamber and supply tank means, whereby coating material liquid discharged into and collected in the collector chamber may be recycled to the supply tank.
 11. The construction defined in claim 1 in which the suction chamber walls are formed of separable upper and lower sections, in which the upper section contains the rear wall means and the front and intermediate collector and suction chamber walls, and in which mounting means is provided for supporting and moving the upper and lower sections toward and away from the backup roll means, whereby said upper section may be detached from the lower section and moved out of normal operating position for access to the interior of said upper section.
 12. The construction defined in claim 1 in which mounting means supports the blowoff box suction and collector chamber walls for movement toward and away from the backup roll means, and in which means is provided for moving said blowoff box walls toward and away from the backup roll means.
 13. The construction defined in claim 1 in which vortex suppressor baffle means are mounted within the collector chamber extending parallel with the axis of the backup roll means, and in which said vortex suppressor baffle means are removably mounted within said collector chamber.
 14. The construction defined in claim 1 in which the air knife means is adjustably mounted to vary its angle of impingement, in which vortex suppressor baffle means extends parallel with the axis of the backup roll means within the collector chamber and below the air knife means, and in which said baffle means is adjustable to coordinate its operation with adjustment of the air knife means.
 15. In a coating apparatus blowoff box construction in which a web traveling along backup means and having a coating applied to one surface moves past air knife means directing in air jet at an angle against the coated web surface; the combination of blowoff box means including rear wall means, and front and end walls forming a suction chamber; walls including an intermediate wall forming a smaller coating material collector chamber within the suction chamber; the collector chamber walls having portions defining a top opening; the suction chamber front and rear wall means having inner edges, the suction chamber end walls having shaped upper edges matching the contour of the backup means, and said upper edges defining a suction chamber top opening at a location spaced above the collector chamber top opening and spaced below a coated web traveling along such backup means; the suction chamber rear wall means being in common the rear wall means of the collector chamber; the suction chamber opening edge at the top of the rear wall means defining in common a portion of the collector chamber opening and being located adjacent and below the air knife means; the intermediate wall having an upper edge defining another portion of the collector chamber opening, and said upper intermediate wall edge being spaced from and substantially close to the front suction chamber wall upper edge defining an opening to a suction chamber passage formed between said front and intermediate walls; suction means for the blowoff box means communicating with said suction chamber passage; spoiler blade means mounted within the blowoff box means extending parallel with the backup means and spaced a fixed distance away from the backup means and Extending transversely of the suction and collector chamber openings and into said suction and collector chambers between said intermediate walls and rear wall means; said spoiler blade means having a flat surface blocking the flow of a substantial portion of air-knife-discharged air which hugs the coated surface of the traveling web passing along said backup means and the mist formed by the air-knife-discharged air entrained by said coated-surface-hugging air, and directing said blocked air and entrained mist into said collector chamber; said spoiler blade means including a first blade having front and rear surfaced and a shaped edges between said front and rear surfaces, the front spoiler blade surface being the flat blocking surface and intersecting the shaped edge at a sharp corner, said shaped edge extending from said sharp corner parallel to tangency with the backup means, and said shaped edge then curving rearwardly downwardly to said rear blade surface. 